Apparatus and method for filling trays

ABSTRACT

One aspect of the present invention relates to an apparatus for filling trays with polymerized growth medium. Another aspect of the present invention relates to a method of filling a tray with polymerized growth medium using an apparatus of the present invention.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/764,271, filed Jan. 23, 2004; which claims the benefit of the filingdate of U.S. Provisional Patent Application Ser. No. 60/442,862, filedJan. 27, 2003; the specifications of all of them are hereby incorporatedin their entirety.

BACKGROUND OF THE INVENTION

Growth plugs are small independent segments of stabilized media whichcan house a variety of biological objects. The plugs typically serve asa medium for plant material, e.g., seeds, seedlings or cuttings, thatwill eventually be transplanted into a new environment. In addition toserving as a growth medium, such plugs can be used for propagation,germination, rooting, micro propagation, clonal propagation, and avariety of in vitro techniques. Growth plugs are commonly used as anenvironment for seeds, seedlings or cuttings, often followed bytransplantation.

Growth plugs usually consist of a block of growth medium, e.g., about 2to 3 inches long and ½ to 1 inch in diameter. The growth medium mayinclude soil, peat, mulch, thatch, sand or any other organic, inorganicor gel substrate, depending on the environment most suited to thecutting, seed or seedling. Typically, the plugs will house a cutting,seed or seedling; however, they can be fashioned to house largergrowths, including saplings and immature shrubs.

The growth plugs provide a compact, economical and stable medium inwhich to house plant material for sale. Most decorative plants andflowers for home gardens are sold in growth plugs. The growth plugs areoften housed in flats or trays constructed of polyethylene, polystyreneor poly(vinyl chloride) (PVC) plastic. This lightweight plastic hasbecome the material of choice for filling flats and trays because it isinexpensive to manufacture and easy to ship and store. Each tray istypically designed as a block with, for example, four to six, traycavities with tapered ends that hold the individual plugs. The bottom ofeach cavity is usually solid, with either a few small holes or one largehole to facilitate drainage from the housed plug. The sides of thecavity may be smooth or porous. Alternatively, open-ended cavities maybe used, to increase airflow around the growth plugs, resulting inbetter growth. The plugs are compressed into the cavities, and,depending on the hardiness of the particular variety of plant, the flatsmay provide a sustainable environment for the cutting, seed or seedlingfor many weeks.

Growth plugs made of composite polymerized medium, such as the mediumdescribed in U.S. Pat. No. 6,322,734, issued to Zanten et al., arefrequently used in growth trays as described above. Such polymerizedgrowth media have many advantages over traditional media, such as soiland peat moss. For example, a polymerized growth plug holds its shapewithout the need for a pot to retain the medium, reducing the cost ofmanufacture and transport. Such polymerized media are typically mixed ina slurry, comprising a mixture of aggregate (including but not limitedto peat, bark, coconut fiber, etc.), water, surfactant (e.g., lecithin,alkylsulfonates or phospholipids), and a polyurethane prepolymer, e.g.,a hydrophilic polyurethane prepolymer. When the prepolymer is mixed withthe other components, the prepolymer begins to polymerize, generatingcarbon dioxide. The carbon dioxide causes the slurry to rise, not unlikea cake rises from gas created by yeast, and the polymerization of theprepolymer stabilizes the resultant substance, not unlike the effect ofegg in a cake. The reaction time is temperature or pH dependent or both;for example, the higher the temperature, the shorter the time it takesthe mixture to rise and polymerize. In a typical reaction at 70 F, themixture begins generating carbon dioxide within approximately five toten seconds after mixing, with full rise within one to two minutes and astable growth plug within approximately six minutes.

Various methods of manufacturing growth plugs are known in the art. U.S.Pat. No. 6,322,734, issued to Zanten et al., describes composition ofpolymerized growth plugs and a method for continuous filling of trays.The components of the polymerized growth medium are combined in a mixerand then emptied into trays as they pass beneath the mixer by means of aconveyor belt. A weighing device measures an appropriate amount ofslurry for the tray being used.

U.S. Pat. No. 5,209,014, issued to Teichmann, discloses the use of a“mold tool” which is filled with composite growth medium, creating agrowth plug or “mold” into which seeds may be planted. The molds arefilled individually, rather than in a tray or array configuration. Usinga rotating table, the molds are passed through various stations in amachine, at which stations components of the composite are added.

U.S. Pat. No. 4,175,355, issued to Dedolph, discloses a method offorming polymerized growth plugs individually in cylindrical molds. Themolds are sprayed with a nonphytotoxic release agent, then individuallyfilled from a nozzle with polymerized growth medium in a slurry form.

U.S. Pat. No. 4,159,727, issued to Visser, discloses a machine forfilling a plurality of individual pots with soil from a hopper as thepots pass underneath the hopper on an endless-chain type conveyor.Excess soil which spills over the tops of the pots is pushed onto anelevator and returned to the hopper.

Also known are methods for filling trays containing multiple traycavities with various thick fluid substances. U.S. Pat. No. 4,747,766,issued to Van Meulenbeke, is directed to a machine for filling trayswith chocolate or another thick fluid substance. It discloses a machinein which trays containing an array of tray cavities pass on a conveyorbelt beneath a tank containing the thick fluid substance. The tankfeatures apertures in its underside that line up with the cavities,allowing the simultaneous filling of an entire row of tray cavities.

Remarkably, the present invention provides a machine and methods to mixthe slurry and deposit it uniformly and quickly into trays, distributingit evenly over multiple tray cavities, such that growth plugs of adesired size, shape, and density may be rapidly and easily produced,before the slurry cures into a firm growth plug. Notably, the machineand methods should provide the flexibility to accommodate trays and traycavities of a variety of sizes, as well as the ability to create growthplugs with different densities to suit the requirements of a widevariety of plant species.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to an apparatus for fillingtrays with polymerized growth medium, comprising: a plurality of feedrollers which propel a tray containing at least one tray cavitydownstream through a filling region; a slurry dispenser nozzle whichdeposits polymerized growth medium in a slurry state on the tray,positioned downstream of the feed rollers; and a filler roller,positioned downstream of the slurry dispenser nozzle, which distributesthe polymerized growth medium into and over the at least one traycavity.

In certain embodiments, the aforementioned apparatus further comprisesat least one brush, positioned downstream of the filler roller, whichremoves excess polymerized growth medium from the tray. In certainembodiments, the at least one brush is a rotary brush.

In certain embodiments, the plurality of feed rollers further comprisesat least one top feed roller positioned above the top surface of a tray,and at least one bottom feed roller positioned below the bottom surfaceof a tray. In certain embodiments of the aforementioned apparatus, thevertical position of the at least one top feed roller is adjustable; andthe vertical position of the at least one bottom feed roller isadjustable independently of the vertical position of the at least onetop feed roller. In certain embodiments of the aforementioned apparatus,the feed rollers rotate at a feed roller rate; the filler roller rotatesat a filler roller rate; and the feed roller rate and the filler rollerrate are independently adjustable.

In certain embodiments, the aforementioned apparatus further comprisesat least one brush, positioned downstream of the filler roller, whichremoves excess polymerized growth medium from the tray, and wherein theplurality of feed rollers further comprises at least one top feed rollerpositioned above the top surface of a tray, and at least one bottom feedroller positioned below the bottom surface of a tray. In certainembodiments of the aforementioned apparatus, the vertical position ofthe at least one top feed roller is adjustable; and the verticalposition of the at least one bottom feed roller is adjustableindependently of the vertical position of the at least one top feedroller. In certain embodiments of the aforementioned apparatus, the feedrollers rotate at a feed roller rate; the filler roller rotates at afiller roller rate; and the feed roller rate and the filler roller rateare independently adjustable.

In certain embodiments of the aforementioned apparatus, the plurality offeed rollers further comprises at least one top feed roller positionedabove the top surface of a tray, and at least one bottom feed rollerpositioned below the bottom surface of a tray. In certain embodiments ofthe aforementioned apparatus, the vertical position of the at least onetop feed roller is adjustable; and the vertical position of the at leastone bottom feed roller is adjustable independently of the verticalposition of the at least one top feed roller.

In certain embodiments, the aforementioned apparatus further comprisesat least one brush, positioned downstream of the filler roller, whichremoves excess polymerized growth medium from the tray. In certainembodiments of the aforementioned apparatus, the at least one brush is arotary brush.

Another aspect of the present invention relates to a method of filling atray with polymerized growth medium using an aforementioned apparatus,comprising feeding a tray containing at least one tray cavity between atleast one top feed roller and at least one bottom roller downstream at atray feed rate through a filling region; depositing the polymerizedgrowth medium in a slurry state from a slurry dispenser nozzle onto thetray; and rotating a filler roller at a filler roller rotation rate todistribute the polymerized growth medium into and over the at least onetray cavity.

In certain embodiments, the aforementioned method further comprisesremoving excess polymerized growth medium with at least one brush.

In certain embodiments, the aforementioned method further comprisesgranulating the removed excess polymerized growth medium and returningit to a mixing chamber from which polymerized growth medium is fed tothe slurry dispenser nozzle.

In certain embodiments, the aforementioned method further comprisescontrolling the density of the polymerized growth medium in the at leastone tray cavity by adjusting the filler roller rotation rate relative tothe tray feed rate.

In certain embodiments, the aforementioned method further comprisesremoving excess polymerized growth medium with at least one brush.

In certain embodiments, the aforementioned method further comprisesgranulating the removed excess polymerized growth medium and returningit to a mixing chamber from which polymerized growth medium is fed tothe slurry dispenser nozzle.

In certain embodiments of the aforementioned method, the tray feed rateis selected so that approximately six minutes elapses between the stepof depositing the polymerized growth medium and the step of removingexcess polymerized growth medium. In certain embodiments of theaforementioned method, the tray feed rate is selected so that thepolymerized growth medium is substantially cured at the time of the stepof removing excess polymerized growth medium.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a schematic side view and face view of an embodiment of atray filling machine of the present invention. FIG. 1A depicts the faceview of an embodiment of a tray filling machine, viewed from theupstream end. FIG. 1B depicts the side view of an embodiment of a trayfilling machine.

FIG. 2 depicts a schematic top view of an embodiment of a tray fillingmachine of the present invention.

FIG. 3 is a photograph of an embodiment of a tray filling machine of thepresent invention.

FIG. 4 is a photograph of an example of a tray after it has been filledusing an embodiment of the tray filling machine of the presentinvention.

FIG. 5 is a photograph of an apparatus of the present invention beingused in a method of the present invention.

FIG. 6 is a photograph of an apparatus of the present invention beingused in a method of the present invention.

FIG. 7 is a photograph of an apparatus of the present invention beingused in a method of the present invention.

FIG. 8 is a photograph of an apparatus of the present invention beingused in a method of the present invention.

FIG. 9 is a photograph of an apparatus of the present invention beingused in a method of the present invention.

FIG. 10 is a photograph of an apparatus of the present invention beingused in a method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

For convenience, certain terms employed in the specification, examplesand claims are collected here.

The term “cavity” means a void or empty space within a body.

The term “growth plug” means an independent segment of stabilized mediaused to act as an environment for seeds or any plant material whichneeds to be in a consistent media prior to transplantation.

The term “polymerized growth medium” means a mixture of aggregate(including but not limited to peat, bark, coconut fiber or othersuitable fibrous material), water, surfactant, and a polyurethaneprepolymer, e.g., a hydrophilic polyurethane prepolymer, used toconstruct growth plugs.

The term “slurry” means polymerized growth medium in its wet, uncuredstate.

The term “stabilized media” or “stabilizing media” means an interveningenvironment through which something functions and thrives that is shapedinto a fixed form which is not easily degraded. Stabilized media caninclude polymerized growth media, organic or inorganic material, or agel substrate.

Overview

The present invention describes an apparatus and methods which allow thefilling of a variety of plant propagating trays with a polymerizedgrowing mix. To provide an overall understanding, certain illustrativeembodiments will now be described; however, it will be understood by oneof ordinary skill in the art that the devices and methods describedherein can be adapted and modified to provide devices and methods forother suitable applications and that other additions and modificationscan be made without departing from the scope of the systems describedherein. The preferred embodiments can best be understood with referenceto the Figures.

Preferred Embodiments

Referring to FIGS. 1A and 1B, the machine consists of a frame in whichare mounted a set of guide rails H, a set of top feed rollers P, and aset of bottom feed rollers J. In the illustrated embodiment, the top andbottom feed rollers are each arranged into arrays of nine rollers each,although other numbers and configurations of rollers may be employed.During operation of the machine, a tray R, containing tray cavities forreceiving polymerized growth medium in slurry form, travels through afilling region defined by the space between the two guide rails. Theguide rails support the tray R as it propagates through the fillingregion, while the feed rollers P and J grip the tray from the top andbottom and impart linear motion to it by rotating in opposingdirections. An advantage of the use of feed rollers over a traditionalconveyor belt arrangement is that the top and bottom feed rollers P andJ grip the tray R with more friction than a conveyor belt. This can helpprevent trays from jamming in the machine, as discussed further below inconnection with the action of the fill roller F on the slurry wave L.

In a preferred embodiment, the top and bottom feed rollers P and J maybe constructed of rubber, a flexible polymer, such as polyvinyl chloride(PVC), or other suitable material, and are inflated with air. The degreeof softness of the rollers may be adjusted by varying the internal airpressure. This feature is important since some trays are fragile, andmay be crushed if gripped too firmly. Alternatively, the top and bottomfeed rollers may be solid, constructed of some suitably soft material,e.g., foam rubber.

In a preferred embodiment, the space between the top feed rollers P andthe bottom feed rollers J can be adjusted to accommodate trays ofvarying thickness. In addition, the adjustment of the top feed rollers Pmay be independent of the adjustment of the bottom feed rollers J, toaccommodate different configurations and to allow varying the meanheight of the tray to optimize the feeding characteristics. In apreferred embodiment, adjustability of the vertical position of the topand bottom feed rollers P and J is achieved by means of a threadedcrank. As illustrated in FIGS. 1A and 1B, the vertical position of thetop feed rollers P may be adjusted by the top feed rollers verticaladjustment crank T, which, when turned, raises and lowers the assemblyin which the top feed rollers P are mounted. The bottom feed rollers Jmay be adjusted similarly and independently by means of bottom feedrollers vertical adjustment V. To further enhance the flexibility of theapparatus, the guide rails H can be easily removed and replaced withothers to match trays of a different profile.

Not shown in the Figures is a mixing chamber, in which the ingredientsof the polymerized growth medium—in a preferred embodiment, a mixture ofaggregate (including but not limited to peat, bark, coconut fiber,etc.), water, surfactant (e.g., lecithin, alkylsulfonates orphospholipids), and a polyurethane prepolymer, e.g., a hydrophilicpolyurethane prepolymer—are combined, forming the slurry. In a preferredembodiment, the mixing chamber is mounted above the apparatus shown inFIGS. 1, 2, and 3. The slurry may be fed directly, or through a hose,from the mixing chamber to the slurry dispenser nozzle S (shown in FIG.1B), provided that the slurry reaches the slurry dispenser nozzle beforerising and curing of the slurry is complete.

In certain embodiments, a bed support plate K may be employed to supportthe tray R during filling. For example, when closed-bottom trays areused, the bed support plate K may provide additional support for thetray during filling. In certain embodiments, such a bed support platealso covers one or more openings at the bottom of an open-ended traycavity, preventing the slurry from leaking out an opening during orafter filling or both.

In certain embodiments, the bed support plate K comprises one or moresurface features, e.g., a pin or rod perpendicular to the surface of theplate, that serve to anchor a tray to the bed support plate or occupy ahole in a tray, e.g., to prevent the slurry from passing through saidhole, or both. For example, certain trays, due to the processes used intheir manufacture, comprise a plurality of holes interspersed amongtheir plurality of cavities; in certain methods of the presentinvention, complementary surface features on a bed support plate willfill the holes, preventing slurry from passing though them.

In still other embodiments, the present invention relates to a pluralityof soil plugs in a nesting feature, and methods of making a nestingfeature charged with a plurality of soil plugs, wherein said nestingfeature comprises a plurality of cavities each comprising in its walls aplurality of holes. Such a cavity charged with a soil plug allows forthe exploitation of air pruning of the roots of, e.g., a seedling, insaid soil plug. For example, bed support plate K comprises or providessupport for a nesting fixture. In general, a nesting fixture comprisesone or more porous cavities, i.e., the surfaces that define the interiorof a cavity comprise pores or holes. In certain embodiments, withrespect to the interior of an individual cavity in the nesting fixture,the combined surface area of the pores is greater than the combinedsurface area of the solid portions of the interior of the cavity. Incertain embodiments, the nesting fixture is removed from the growthplugs after polymerization of the slurry, providing growth plugs thatare not housed in a tray or its equivalent. In certain embodiments, theuse of a nesting fixture will allow the preparation of a growth plug ina shape or size or both that would be difficult or impossible to prepareusing conventional trays, e.g., because the technology used to fabricatethe trays is incapable of providing trays comprising cavities of theshape or size or both. In general, a relatively small number of nestingfixtures will be sufficient for the preparation of a large number ofgrowth plugs because the growth plugs are removed from the nestingfixtures after polymerization of the slurry.

In certain embodiments, after the tray R passes through the top andbottom feed rollers P and J, it engages the bed support plate K,positioned under the fill roller F and extending upstream and downstreamfrom the fill roller F through the filling region for a distancesufficient to accommodate the length of the tray being filled. The fillroller F is mounted above the bed support plate. In one embodiment, thefill roller F is mounted approximately fifteen inches downstream fromthe last feed roller. The fill roller F is motor driven and turns sothat its lowermost point moves in the same direction as the tray R. Thefunction of the fill roller F is to distribute the slurry over and intothe tray cavities. A slurry dispenser nozzle S deposits the slurry infront of the fill roller F, forming a slurry wave L which the fillroller F rolls over and into the cavities. The wave is contained fromside to side by baffles M, which may be adjustable to accommodatedifferent tray widths.

The rotation rate of the fill roller F, as well as tray feed rate (therate of linear travel of the tray R), may be independently adjustable.Varying the rotation rate of the fill roller F is one method ofcontrolling the density of the growth plugs formed as the tray isfilled. If the feet per minute rate of the circumference of the feedroller F exceeds the tray feed rate at the feed roller F, there is atendency to pack more slurry into the tray cavities and thus create amore dense plug. Conversely, if the feed roller F rotates at a slowerrate, such that the feet per minute rate of the circumference of thefeed roller F is less than the tray feed rate at the feed roller F, theresulting growth plugs will be less dense. In a preferred embodiment,the fill roller has a vertical adjustment and can be set so as to makecontact with the tray or, if desired, be raised above the tray so as tonot only fill the cavities, but leave a mat of material above the top ofthe tray.

The action of the fill roller F upon the slurry wave L in pressing theslurry down into the tray cavities pushes down and back against the trayR, impeding its smooth advancement through the filling region. If aconveyor belt were used, the tray R would tend to stick beneath theslurry wave L, ceasing to advance as the conveyor belt slipped beneaththe tray R. The use of the feed rollers J and P to propel the tray Rthough the filling region, rather than traditional conveyor means, canhelp combat the tendency of the tray R to stick. Because the feedrollers J and P grip the tray R with greater friction than a conveyorbelt, they help ensure continuous forward motion of the tray R throughthe filling region, beneath the slurry wave L and fill roller F.

Because the rate at which the slurry rises and cures is dependent uponthe temperature of the reaction, by controlling the temperature or thepH of the reactants or both, the feed rate of the trays through thefilling machine, and the location of the slurry dispense nozzle S, onecan control the degree to which the slurry has risen at the time it isrolled into the tray cavities. In a preferred embodiment, the slurry is75% to 85% risen before it is rolled into the tray cavities, and thencontinues to rise after the cavities are filled, such that by the timethe product is stabilized (e.g., six minutes), it protrudes above thetray cavity to a thickness of about 1/32 to 1/16 inch. The excess maythen be removed by brushes N, which also granulate the removed materialso it can be added back into the next aggregate batch. In someembodiments, an elevator, conveyor, or similar means may be employed tocollect the excess polymerized growth medium and return it to the mixingchamber to be used in the formation of additional slurry. In theembodiment illustrated in FIGS. 1 and 2, the brushes N arecounter-rotating rotary brushes; alternatively, brushes arranged onrollers or brushes that move laterally may be employed. The brushingprocedure also removes any “skin” that may have formed on the topsurface during curing, leaving an open-celled top surface that willreadily accept water. In a preferred embodiment, the vertical clearanceof the brushes N can be adjusted, such that after the excess material isremoved the resultant plug is flush with the top of the tray or recessedbelow the top, depending on the configuration desired. In certainembodiments, the growth plugs are punctured or dibbled to facilitate thedeposit of seeds, seedlings, or cuttings; this modification may beperformed at any point prior to depositing the seeds, seedlings, orcuttings.

EXEMPLIFICATION

The invention now being generally described, it will be more readilyunderstood by reference to the following examples, which are includedmerely for purposes of illustration of certain aspects and embodimentsof the present invention, and are not intended to limit the invention.

Example

Using the apparatus and methods described herein, a lot of 300 LandmarkP-72 round cavity propagation trays were filled. This tray is a typicalplug tray used in the greenhouse industry, which measures approximately11 inches wide by 21 inches long and contains 72 cavities of 1¼ inchdiameter by 1½ inch deep, configured in rows of six by twelve.

The trays were fed end to end through the tray-filling machine at a rateof 18 seconds per tray or 5.8 ft/min, and filled with media comprising amix of 44% peat/water slurry, 44% composted bark/water slurry, and 12%hydrophilic urethane prepolymer. The temperature of the mix was between87 F and 91 F with a pH of 5.6. The composted bark was previouslygranulated to a particle size of approximately ⅛ inch. The fill rollerwas set at a rate of 10.71 rpm, or 6.66 ft/min at the circumference.

The resultant filled trays were allowed to cure for approximately sixminutes. After curing, any residual media was removed from the tray topsby rotary brushes, leaving the balance in the filled cavity flush withthe tray surface. The filled cavities were then dibbled with a sixmillimeter pin to a depth of ⅝ inch to form a receptacle for insertingvegetative cuttings. A sampling of the completed plugs were removed fromthe trays and inspected for uniformity and integrity. The machinesettings listed above yielded plugs with a density of 2.3 g/cc. Thetrays were then palletized and shipped.

ADDITIONAL PATENTS AND PUBLICATIONS CITED

-   1. U.S. Pat. No. 4,159,727.-   2. U.S. Pat. No. 4,175,355.-   3. U.S. Pat. No. 4,747,766.-   4. U.S. Pat. No. 4,947,582.-   5. U.S. Pat. No. 5,068,999.-   6. U.S. Pat. No. 5,207,733.-   7. U.S. Pat. No. 5,209,014.-   8. U.S. Pat. No. 6,322,734.

INCORPORATION BY REFERENCE

All of the patents and publications cited herein are hereby incorporatedby reference.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

1. An apparatus for filling trays with polymerized growth medium,comprising: a plurality of feed rollers which propel a tray containingat least one tray cavity downstream through a filling region; a slurrydispenser nozzle which deposits polymerized growth medium in a slurrystate on the tray, positioned downstream of the feed rollers; and afiller roller, positioned downstream of the slurry dispenser nozzle,which distributes the polymerized growth medium into and over the atleast one tray cavity.
 2. The apparatus of claim 1, further comprisingat least one brush, positioned downstream of the filler roller, whichremoves excess polymerized growth medium from the tray.
 3. The apparatusof claim 2, wherein the at least one brush is a rotary brush.
 4. Theapparatus of claim 1, wherein the plurality of feed rollers furthercomprises at least one top feed roller positioned above the top surfaceof a tray, and at least one bottom feed roller positioned below thebottom surface of a tray.
 5. The apparatus of claim 4, wherein: thevertical position of the at least one top feed roller is adjustable; andthe vertical position of the at least one bottom feed roller isadjustable independently of the vertical position of the at least onetop feed roller.
 6. The apparatus of claim 1, wherein: the feed rollersrotate at a feed roller rate; the filler roller rotates at a fillerroller rate; and the feed roller rate and the filler roller rate areindependently adjustable.
 7. The apparatus of claim 1, furthercomprising at least one brush, positioned downstream of the fillerroller, which removes excess polymerized growth medium from the tray,and wherein the plurality of feed rollers further comprises at least onetop feed roller positioned above the top surface of a tray, and at leastone bottom feed roller positioned below the bottom surface of a tray. 8.The apparatus of claim 7, wherein: the vertical position of the at leastone top feed roller is adjustable; and the vertical position of the atleast one bottom feed roller is adjustable independently of the verticalposition of the at least one top feed roller.
 9. The apparatus of claim8, wherein: the feed rollers rotate at a feed roller rate; the fillerroller rotates at a filler roller rate; and the feed roller rate and thefiller roller rate are independently adjustable.
 10. The apparatus ofclaim 6, wherein the plurality of feed rollers further comprises atleast one top feed roller positioned above the top surface of a tray,and at least one bottom feed roller positioned below the bottom surfaceof a tray.
 11. The apparatus of claim 10, wherein: the vertical positionof the at least one top feed roller is adjustable; and the verticalposition of the at least one bottom feed roller is adjustableindependently of the vertical position of the at least one top feedroller.
 12. The apparatus of claim 11, further comprising at least onebrush, positioned downstream of the filler roller, which removes excesspolymerized growth medium from the tray.
 13. The apparatus of claim 12,wherein the at least one brush is a rotary brush.
 14. A method offilling a tray with polymerized growth medium using an apparatus ofclaim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13, comprising: feedinga tray containing at least one tray cavity between at least one top feedroller and at least one bottom roller downstream at a tray feed ratethrough a filling region; depositing the polymerized growth medium in aslurry state from a slurry dispenser nozzle onto the tray; and rotatinga filler roller at a filler roller rotation rate to distribute thepolymerized growth medium into and over the at least one tray cavity.15. The method of claim 14, further comprising removing excesspolymerized growth medium with at least one brush.
 16. The method ofclaim 15, further comprising granulating the removed excess polymerizedgrowth medium and returning it to a mixing chamber from whichpolymerized growth medium is fed to the slurry dispenser nozzle.
 17. Themethod of claim 14, further comprising controlling the density of thepolymerized growth medium in the at least one tray cavity by adjustingthe filler roller rotation rate relative to the tray feed rate.
 18. Themethod of claim 17, further comprising removing excess polymerizedgrowth medium with at least one brush.
 19. The method of claim 18,further comprising granulating the removed excess polymerized growthmedium and returning it to a mixing chamber from which polymerizedgrowth medium is fed to the slurry dispenser nozzle.
 20. The method ofclaim 18, wherein the tray feed rate is selected so that approximatelysix minutes elapses between the step of depositing the polymerizedgrowth medium and the step of removing excess polymerized growth medium.21. The method of claim 19, wherein the tray feed rate is selected sothat approximately six minutes elapses between the step of depositingthe polymerized growth medium and the step of removing excesspolymerized growth medium.
 22. The method of claim 18, wherein the trayfeed rate is selected so that the polymerized growth medium issubstantially cured at the time of the step of removing excesspolymerized growth medium.
 23. The method of claim 19, wherein the trayfeed rate is selected so that the polymerized growth medium issubstantially cured at the time of the step of removing excesspolymerized growth medium.